Hydroprocessing catalyst and method for preparing it

ABSTRACT

Hydroprocessing of hydrocarbon oils is carried out utilizing a catalyst containing active metal components on a porous refractory oxide and having a narrow pore size distribution, with essentially all pores being of diameter greater than about 100 angstroms, with less than about 10 percent of the total pore volume being in pores of diameter greater than 300 angstroms, and with at least about 60 percent of the total pore volume being in pores of diameter from about 180 to about 240 angstroms. The catalyst is particularly useful for removing of contaminant metals from residuum hydrocarbon oils.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to catalysis, and particularly to hydrocarbonhydroprocessing catalysts, such as those utilized to catalyze thereaction of hydrogen with organosulfur, organonitrogen, organometallicand asphaltene compounds. More particularly, this invention relates to ahydroprocessing catalyst and a process for utilizing the catalyst forhydrodesulfurizing, hydrodemetallizing and converting asphaltenecompounds in hydrocarbon liquids.

2. Description of the Prior Art

In a typical catalytic hydrocarbon refining process, contaminant metalscontained in a hydrocarbon oil deposit on porous refining catalysts,causing a gradual loss of catalytic activity and/or selectivity foryielding an intended product. Residual petroleum oil fractions, such asthe heavy fractions produced in atmospheric and vacuum crudedistillation columns, are especially undesirable as feedstocks for mostcatalytic refining processes due to their high metals, asphaltene andsulfur content. Economic considerations, however, have recently providednew incentives for catalytically converting the heavy fractions to moremarketable products.

Methods are available to reduce the sulfur, metals and asphaltenecontent of residua. One such method is hydrodesulfurization, a processwherein a residuum, usually containing the bulk of the asphaltenecomponents of the original crude from which the residuum was derived, iscontacted with a catalyst usually containing hydrogenation metals on aporous refractory oxide support under conditions of elevated temperatureand pressure and in the presence of hydrogen such that the sulfurcomponents are converted to hydrogen sulfide, and the asphaltenecomponents to lower molecular weight molecules while the metals aresimultaneously deposited on the catalyst. However, the deposition ofcontaminant metals on the catalyst causes deactivation of the catalyst,and, in the usual instance, the extent of deactivation is a function ofthe amount of metals deposition on the catalyst surface, i.e., theusefulness of the catalyst steadily decreases as the amount of depositedmetals increases with continued treatment of the residuum.

It has been recognized that typical hydroprocessing catalysts,especially those utilized for hydrodesulfurization purposes, havespecific pore size characteristics effective for catalytic processing ofresiduum. For example, a catalyst employed in a two-catalysthydrodesulfurization process ordinarily includes at least onedesulfurization catalyst having a sizable number of pores of diameterless than 100 angstroms. Although such a catalyst often exhibits highdesulfurization activity, its useful life is manifestly short in theabsence of a catalyst promoting metals removal. Conversely, manycatalysts exhibiting a suitable degree of demetallation activity tend tohave a sizable number of pores having a diameter greater than 300angstroms. The hydrodesulfurization processes disclosed in U.S. Pat.Nos. 3,819,509 and 3,901,792 are typical of a catalyst having relativelysmall pore characteristics (i.e. some pore diameters less than 100angstroms) for desulfurization and a second relatively large porecatalyst additionally promoting metals removal.

Although conventional catalysts, including those containing both largepores (i.e., greater than 300 angstroms pore diameters) and small pores(i.e., less than 100 angstroms pore diameters) are somewhat active andstable for hydrocarbon conversion reactions, catalysts of yet higheractivities and stabilities are still being sought. Increasing theactivity of a catalyst increases the rate at which a chemical reactionproceeds under given conditions, and increasing the stability of acatalyst increases its resistance to deactivation, that is, the usefullife of the catalyst is extended. In general, as the activity of acatalyst is increased, the conditions required to produce a given endproduct, such as a hydrocarbon of given sulfur, asphaltene, and/orcontaminant metals content, become more mild. Milder conditions requireless energy to achieve the desired product, and catalyst life isextended due to such factors as lower coke formation or the depositionof less metals.

Presently, conventional catalysts employed to promote a suitable degreeof hydrodesulfurization of a hydrocarbon oil tend to have limitedcapability for also removing contaminant metals and/or convertingasphaltenes to less complex components. Although, such conventionalcatalysts may be active for removing sulfur, the useful life of suchcatalysts may be relatively short when high demetallization activityand/or asphaltene conversion is also emphasized.

A need still exists for a highly active hydroprocessing catalyst with anextended useful life when employed to promote hydrocarbon conversionreactions, particularly hydrodesulfurization, hydrodemetallizationand/or hydroconversion of asphaltenes.

Accordingly, it is an object of the present invention to provide a novelhydroprocessing catalyst that is highly active and still has a longuseful life when employed in catalytic hydrocarbon conversion processesto promote the upgrading of a hydrocarbon oil, particularly with respectto removing contaminant metals in addition to sulfur compounds.

It is another object to provide a novel catalyst that may be employed ina process for hydrodesulfurizing a hydrocarbon oil while maintaining ahigh degree of demetallization.

It is still another object of the invention to provide a novel catalystfor hydrodemetallizing a hydrocarbon oil and specifically, to provide anovel catalyst with a high capacity for accumulating contaminant metals.

It is a further object of the invention to provide novel processes forthe hydrodemetallization, hydrodesulfurization and hydroconversion ofasphaltenes found in heavy hydrocarbon oil fractions.

These and other objects and advantages of the invention will becomeapparent from the following description.

SUMMARY OF THE INVENTION

The present invention is directed to a catalyst and a process for thecatalytic hydroprocessing of a hydrocarbon oil. The catalyst has anarrow pore size distribution wherein essentially all the pores are ofdiameter greater than 100 angstroms, less than 10 percent of the totalpore volume is in pores of diameter greater than 300 angstroms, and atleast about 60 percent of the total pore volume is in pores of diameterbetween about 180 and about 240 angstroms. Generally, the catalystcontains one or more active metal components, typically Group VIB andGroup VIII hydrogenation metal components in combination, on a porousrefractory oxide support material usually containing alumina.Ordinarily, the catalyst is utilized to enhance the removal ofsubstantial amounts of metal contaminants in addition to conversion ofasphaltenes and sulfur compounds from a metals-containing hydrocarbonoil.

In one embodiment, the catalyst has a surface area between about 100 m²/gram and about 200 m² /gram and a total pore volume between about 0.25cc/gram and about 1.2 cc/gram. When employed in the hydroprocessing of ametals-containing hydrocarbon oil, the catalyst is highly active andstable, due in part to a particularly large capacity for accumulatingcontaminant metals.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a hydroprocessing catalyst comprisingactive metals on a support, and more preferably, to hydrodesulfurizationcatalysts comprising Group VIII and VIB active metal components on anon-zeolitic support comprising porous refractory oxide material. Thecatalyst of the invention is particularly well suited forhydrodesulfurization wherein the desired result is desulfurizationcoupled with a high degree of hydroconversion of asphaltenes and/orhydrodemetallation of a hydrocarbon oil containing a high content ofmetallic contaminants, asphaltenes and sulfur.

Porous refractory oxides useful in the present hydroprocessing catalystsinclude silica, magnesia, silica-magnesia, zirconia, silica-zirconia,titania, silica-titania, etc. Mixtures of the foregoing oxides are alsocontemplated, especially when prepared as homogeneously as possible. Thepreferred refractory oxide material, however, comprises aluminum and isusually selected from the group consisting of alumina, lithium-alumina,phosphorus-alumina, lithium-phosphorus-alumina, and silica-alumina. Whenemployed in the preparation of catalysts promoting hydrocarbonconversion processes such as hydrodesulfurization, hydrodemetallizationand hydroconversion of asphaltenes, transition aluminas such as gammaalumina, delta alumina and theta alumina are highly preferred refractoryoxides. It is most highly preferred that the porous refractory oxidecontaain at least about 90, and even more preferably at least about 95weight percent of gamma alumina.

The support material is usually prepared in the form of shapedparticulates by methods well known in the art, with the preferred methodbeing to extrude a precursor of the desired support, as for example, aninorganic refractory oxide gel such as a spray-dried or peptized aluminagel, through a die having openings therein of desired size and shape,after which the extruded matter is cut into extrudates of desiredlength. The particles have a symmetrical cross-sectional shape, and theaverage length of the particles is at least twice that of thecross-sectional diameter. The cross-sectional diameter is hereinconsidered as the longest dimension on the cross-section takenperpendicular to the longest axis of symmetry of the particle. Preferredrefractory oxide particles have cross-sectional shapes that arecylindrical or have protrusions (lobes) from a central area, such aspolylobes. The cross-sectional diameter of the particles is usuallyabout 1/40 to about 1/8 inch, preferably about 1/32 to about 1/12 inch,and most preferably about 1/24 to about 1/15 inch. Among the preferredrefractory oxide particles, at least for hydroprocessing, are thosehaving cross-sectional shapes resembling that of a three-leaf clover, asshown, for example, in FIGS. 8 and 8A of U.S. Pat. No. 4,028,227.Preferred clover-shaped particulates are such that each "leaf" of thecross-section is defined by about a 270° arc of a circle having adiameter between about 0.02 and 0.04 inch. More preferred particulatesare those having cross-sectional shapes that are quadralobal, as in FIG.10 of U.S. Pat. No. 4,028,227, and most preferably, when the lobes arisefrom circles of equal diameter having their centers at the vertices of arhombus having diagonals intersecting at the center of thecross-section.

Support particles prepared by the foregoing or equivalent procedures aregenerally precalcined, especially if gamma alumina is the chosen supportmaterial. Temperatures above about 900° F. are usually required toconvert alumina gel or hydrated alumina particulates to gamma alumina.Typically, temperatures between about 1,100° F. and 1,500° F. areutilized to effect this transformation, with holding periods of 1/4 to 3hours generally being effective.

Physical characteristics of the support particles utilized to preparethe catalyst of the invention typically include a narrow pore sizedistribution wherein essentially all the pores are of diameter greaterthan 100 angstroms, less than about 10 percent of the total pore volumeis in pores of diameter greater than 300 angstroms, and at least about60 percent, preferably at least about 65 percent, of the total porevolume is in pores of diameter distributed over a narrow range of about60 angstroms within the 100 angstrom range of about 140 to about 240angstroms, as determined by conventional mercury porosimeter testingmethods.

Since the present catalysts require at least 60 percent of their porevolume to be in pores of 180 to 240 angstrom diameter, it will be seenfrom the foregoing that, in the preparation of the catalysts of thepresent invention, the support particles may initially have a similardistribution of pore volume as the final catalyst, but such is notnecessary or critical. As will be shown hereinafter in Example I, thesupport particles may have, for example, at least 60 percent of theirpore volume in pores of 140 to 200 angstrom diameter and yet still, dueto the subsequent impregnations, calcinations, and other catalystpreparational steps hereinafter discussed, yield a final catalysthaving, as required herein, at least 60 percent of the pore volume inpores of 180 to 240 angstrom diameter.

Other characteristics of supports utilized herein include a total porevolume, an average pore diameter and surface area large enough toprovide substantial space and area to deposit the active metalcomponents. The total pore volume of the support, as measured by theconventional mercury/helium differential density method, is usuallyabout 0.5 to about 2.0 cc/gram, preferably about 0.5 to about 1.5cc/gram, and most preferably about 0.7 to about 1.1 cc/gram. The averagepore diameter of the support is usually greater than about 160angstroms, and preferably from about 160 to about 220 angstroms.Additionally, the surface area (as measured by the B.E.T. method) of thesupport particles is above about 100 m² /gram, usually from about 100 m²/gram to about 300 m² /gram, and preferably about 125 m² /gram to about275 m² /gram.

Support particles having the preferred physical characteristicsdisclosed herein are commercially available from Armak Catalyst Divisionof Akzona, Inc.

To prepare the hydroprocessing catalyst, the support material iscompounded, as by impregnation of calcined support particles, with oneor more precursors of a catalytically active metal or metals. Theimpregnation may be accomplished by any method known in the art, as forexample, by spray impregnation wherein a solution containing the metalprecursors in dissolved form is sprayed onto the support particles.Another method is the circulation or multi-dip procedure wherein thesupport material is repeatedly contacted with the impregnating solutionwith or without intermittent drying. Yet another method involves soakingthe support in a relatively large volume of the impregnation solution,and yet one more method, the preferred method, is the pore volume orpore saturation technique wherein support particles are introduced intoan impregnation solution of volume just sufficient to fill the pores ofthe support. On occasion, the pore saturation technique may be modifiedso as to utilize an impregnation solution having a volume between 10percent less and 10 percent more than that which will just fill thepores.

If the active metal precursors are incorporated by impregnation, asubsequent or second calcination, as for example, at temperaturesbetween 900° F. and 1,400° F., converts the metals to their respectiveoxide forms. In some cases, subsequent calcinations may follow theimpregnation of individual active metals. Subsequent calcinations,however, may be avoided in alternative embodiments of the invention, asfor example, by comulling the active metals with the support materialrather than impregnating the metals thereon. In comulling, the precursorof the support material, usually in a hydrated or gel form, is admixedwith precursors of the active metal components, either in solid form orin solution, to produce a paste suitable for shaping by known methods,e.g., pelleting, extrusion, etc. A subsequent calcination yields ahydroprocessing catalyst containing the active metals in theirrespective oxide forms.

When the hydroprocessing catalyst is prepared by the foregoing orequivalent methods, at least one active metal component is usuallyselected and typically from the Group VIB and VIII metals of thePeriodic Table of Elements. Preferably, the catalyst contains both aGroup VIB and VIII element, with nickel and cobalt being the preferredGroup VIII metals and molybdenum and tungsten being the preferred GroupVIB metals, and with cobalt and molybdenum in combination being the mostpreferred active metals for a hydrodesulfurization catalyst, andparticularly for hydrodemetallization. Also, nickel and tungsten incombination are highly preferred for hydroconversion of asphaltenecompounds. The hydroprocessing catalyst contains up to about 10, usuallyfrom 1 to 8 percent, and preferably from 2 to 6 percent by weight of theGroup VIII metal, calculated as the monoxide, and up to about 30,usually from about 3 to about 28 percent, and preferably from 8 to 26percent by weight of the Group VIB metal, calculated as the trioxide.

In accordance with the invention, a hydroprocessing catalyst is preparedso as to have a narrow pore size distribution wherein essentially allthe pores are of diameter greater than about 100 angstroms, less thanabout 10 percent of the total pore volume is in pores of diametergreater than about 300 angstroms, and at least about 60 percent, andpreferably at least about 65 percent, of the total pore volume is inpores of diameter from about 180 to about 240 angstroms. Other physicalproperties of the catalyst typically include a total pore volume ofusually less than about 1.2 cc/gram and a surface area greater thanabout 100 m² /gram, with both properties determined by the conventionalmethods previously disclosed herein. Physical characteristics of thecatalyst of the invention including pore size distribution, average porediameter, surface area, total pore volume and average crush strength aresummarized in Table I.

                  TABLE I                                                         ______________________________________                                        PHYSICAL CHARACTERISTICS                                                      OF CATALYST                                                                               % of Total Pore Volume                                            Pore Size Distribution                                                                      Broad    Preferred                                                                              Most Preferred                                ______________________________________                                        <100            0        0        0                                           >140          --       --       >95                                           >150          --       >90      >90                                           180-240       >60      >65      >70                                           180-220       >30      >40      >50                                           >240          --       --       <25                                           >300          <10      <10      <10                                           >500          --       --        <6                                           Average pore diameter,                                                                      >180     180-220  190-210                                       angstroms                                                                     Surface area, m.sup.2 /gram                                                                 >100     100-200  110-190                                       Total pore volume,                                                                          0.25-1.2 0.4-0.9  0.45-0.8                                      cc/gram                                                                       Average crush strength                                                                       >4       >7      >10                                           lbs / 1/8 inch                                                                ______________________________________                                    

A highly preferred catalyst of the invention contains about 2 to about 6weight percent of Group VIII metal components, calculated as themonoxide, and from 10 to about 16 weight percent of Group VIB metalcomponents, calculated as the trioxide, on a porous refractory oxidesupport consisting essentially of gamma alumina. The most preferredGroup VIII and Group VIB metals in this embodiment are cobalt andmolybdenum, respectively. Physical characteristics of this catalystinclude a total pore volume of about 0.6 to about 0.8 cc/gram, a surfacearea from about 110 to about 190 m² /gram and an average pore diameterfrom about 190 to about 210 angstroms.

Another highly preferred catalyst of the invention contains about 2 toabout 6 weight percent of Group VIII metal components, calculated as themonoxide, and from about 18 to about 26 weight percent of Group VIBmetal components, calculated as the trioxide, on a porous refractoryoxide consisting essentially of gamma alumina. Most preferably, theGroup VIII metal is nickel and the Group VIB metal is tungsten. Physicalproperties of this catalyst include a total pore volume of about 0.45 toabout 0.75 cc/gram, a surface area between about 110 and 190 m² /gramand an average pore diameter from about 190 to about 210 angstroms.

An unusual porosity feature of the catalyst is the combination of atleast three critical characteristics. First, the catalyst is prepared sothat few, if any, small pores are present. Essentially all the pores ofthe catalyst are of diameter greater than about 100 angstroms (e.g.,essentially no micropores less than about 100 angstroms), preferablymore than about 90 percent of the total pore volume is in pores ofdiameter greater than 150 angstroms, and most preferably more than about95 percent of the total pore volume is in pores of diameter greater thanabout 140 angstroms. These relatively large pores in the catalystprovide essentially free access to the active catalytic sites for thelarge aromatic polycyclic molecules, such as asphaltenes, in which asubstantial proportion of the metallic contaminants in hydrocarbon oilresidua is usually contained. Second, less than 10 percent of the totalpore volume of the catalyst is in pores of diameter greater than 300angstroms, including preferably less than about 6 percent in pores ofdiameter greater than 500 angstroms, and more preferably less than 25percent of the total pore volume being in pores of diameter greater than240 angstroms. Minimizing the number of macropores (300 angstromdiameter or larger) in the catalyst contributes to maximizing theavailable surface area for active catalytic sites. Third, the catalysthas at least about 60 percent, preferably at least about 65 percent, andmost preferably at least about 70 percent of the total pore volume inpores of diameter in the range from about 180 angstroms to about 240angstroms. Since such a large percentage of the pore volume isdistributed in medium-sized pores of diameter from about 180 to about240 angstroms, the number of macropores and micropores is substantiallyminimized so that the bulk of the available surface area is distributedin the medium-sized pores. It is theorized, at least forhydrodemetallization purposes, that both the size and the substantialnumber of pores in the medium-size range allows for both readypenetration into the catalyst by relatively large metals-containingmolecules and deposition of a significant amount of contaminant metalson the walls and mouth of each pore; and invention, however, is notlimited to this or any other theory of operation.

An unusual feature of the catalyst of the invention is the moreefficient utilization of the pore volume of the catalyst particles asevidenced by similar contaminant metals concentration on the exteriorsurface of a particle and at a substantial depth within the particle.Such similar metals concentrations may be determined analytically usinga scanning electron microscope (SEM) to produce line scans traversing across-sectional plane of a catalyst particle between a point on itsexterior surface and a point at a substantial depth within. Forpreferred catalyst particles having at least one symmetricalcross-section, a substantial depth is determined by reference to aperpendicular plane bisecting the longest axis of symmetry. On thiscross-section, those points which are everywhere equidistant from theperimeter while defining a similar shape as the cross-section butencompassing only 25 percent of its area are points which are consideredherein to lie at a substantial depth within the particle. Line scanexaminations of such cross-sections after the particles have beenremoved during a hydroprocessing run, as well as at or near the end ofthe run, reveal that the concentration of contaminant metals at thedescribed depth will typically average at least 75 percent, preferablybetween 85 and 125 percent, and most preferably between 90 and 110percent of the concentration of the contaminant metals on the surface ofthe particle. The same relative percentages of metals concentrationbetween the exterior and an internal depth location apply tocorresponding points on surfaces of imaginary internal and actualexterior volumes of similar shape for catalyst particles having nosymmetrical cross-section. However, the depth within the particle isdetermined from the imaginary internal volume, having a surface ofpoints everywhere equidistant from corresponding points on the actualexterior of the particle, but encompassing only 50 percent of the actualexterior volume of the particle. It is theorized that the superioractivity and/or stability properties of the catalyst of the inventionfor promoting the hydroprocessing of hydrocarbon oils is attributable inpart to a more efficient utilization of the pore volume for allowingpenetration and accumulation of contaminant metals. Such relativepercentages of metals concentrations have been found to particularlypertain to the catalyst of the invention when utilized in a firstreactor in the hydroprocessing of a hydrocarbon oil when at least about35 percent of the total pore volume is distributed in pores of diameterin a preferred range of about 180 to about 220 angstroms.

Catalysts prepared in accordance with the invention are employed underhydroprocessing conditions suited for their intended purposes, as forexample, in a process for upgrading hydrocarbon oils such ashydrocracking, hydrotreating, hydrodemetallization, orhydrodesulfurization with usual conditions being an elevated temperatureabove 600° F., a pressure above 500 p.s.i.g., and the presence ofhydrogen. Such catalysts are also activated in accordance with methodssuited to such catalysts. As an illustration, most hydroprocessingcatalysts are more active, sometimes even far more active, in a sulfidedor reduced form than in the oxide form in which they are generallyprepared. Accordingly, hydroprocessing catalysts prepared in accordancewith the invention may be sulfided or reduced prior to use (in whichcase the procedure is termed "presulfiding" or "prereducing") by passinga sulfiding or reducing gas, respectively, over the catalyst prepared inthe calcined form. Temperatures between 300° F. and 700° F. and spacevelocities between about 150 and 500 v/v/hr are generally employed, andthis treatment is usually continued for about two hours. Hydrogen may beused to prereduce the catalyst while a mixture of hydrogen and one ormore components selected from the group consisting of sulfur vapor andthe sulfur compounds (e.g., lower molecular weight thiols, organicsulfides, and especially H₂ S) is suitable for presulfiding. Generallyspeaking, the relative proportion of hydrogen in the presulfidingmixture is not critical, with any proportion of hydrogen ranging between1 and 99 percent by volume being adequate.

If the catalyst is to be used in a sulfided form, it is preferred that apresulfiding procedure be employed. However, since many hydroprocessingcatalysts are used to upgrade sulfur-containing hydrocarbons, as inhydrodesulfurization, one may, as an alternative, accomplish thesulfiding in situ, particularly with hydrocarbon oils containing about1.0 weight percent or more of sulfur under conditions of elevatedtemperature and pressure.

Preferably the catalyst is employed in a process for thehydrodesulfurization of hydrocarbon oils, particularly where the processalso emphasizes a high degree of hydrodemetallization and/orhydroconversion of asphaltenes. The catalyst is usually employed aseither a fixed or fluidized bed of particulates in a suitable reactorvessel wherein the oils to be treated are introduced and subjected toelevated conditions of pressure and temperature, and a substantialhydrogen partial pressure, so as to effect the desired degree ofdesulfurization, denitrogenation, asphaltene conversion anddemetallization. Most usually, the catalyst is maintained as a fixed bedwith the oil passing downwardly therethrough. It is highly preferredthat the catalyst be utilized in a train of several reactors requiredfor severe hydrodesulfurization, as for example, in a multiple trainreactor system having one or two reactors loaded with the catalyst ofthe invention and the remaining reactors with one or more otherhydroprocessing catalysts. Alternatively, the catalyst of the inventionmay be loaded in a single reactor together with one or more otherhydroprocessing catalysts. The catalyst of the invention is employedalone or with other hydroprocessing catalysts in reactors that aregenerally operated under the same or an independent set of conditionsselected from those shown in the following Table II:

                  TABLE II                                                        ______________________________________                                        Operating Conditions                                                                         Suitable Range                                                                            Preferred Range                                    ______________________________________                                        Temperature, °F.                                                                      500-900     600-850                                            Hydrogen Pressure,                                                                             500-3,000 1,000-2,500                                        p.s.i.g.                                                                      Space Velocity, LHSV                                                                         0.05-3.0    0.1-1.5                                            Hydrogen Recycle Rate,                                                                        1,000-15,000                                                                              2,000-10,000                                      scf/bbl                                                                       ______________________________________                                    

Contemplated for treatment by the process employing the catalyst of theinvention are hydrocarbon-containing oils, herein referred to generallyas "oils," including broadly all liquid and liquid/vapor hydrocarbonmixtures such as crude petroleum oils and synthetic crudes. Among thetypical oils contemplated are top crudes, vacuum and atmosphericresidual fractions, heavy vacuum distillate oils, shale oils, oils frombituminous sands, coal compositions, and the like, which contain sulfurand one or more of such contaminant metals as vanadium, nickel, iron,sodium, zinc, and copper. Typically, sulfur and metals-containinghydrocarbon oils, preferably containing at least about one weightpercent of sulfur and in excess of 2 ppmw of total contaminant metals,are treated in the presence of the catalyst of the invention. Since themetallic poisons which deactivate hydrocarbon refining catalysts aregenerally associated with the asphaltene components of the oil, thecatalyst will be more commonly employed during the hydroprocessing ofthe higher boiling fractions (e.g., residua) in which the asphaltenecomponents concentrate. The process utilizing the catalyst of theinvention is especially useful for treating oils containing more thanabout 25 ppmw, and preferably, more than 100 ppmw of nickel plusvanadium contaminant metals, and between about 1 and 8 weight percent ormore of sulfur, as for example, atmospheric and vacuum distillationresidua which contain a substantial proportion of asphaltenes. Thetypical residuum for treatment herein is high boiling (i.e., at least95% of its constituents boil above about 600° F.) and often containsundesirable proportions of nitrogen, usually in a concentration betweenabout 0.2 and 0.4% by weight. Such sulfur, nitrogen, asphaltene andmetals-containing oils commonly have an API gravity less than about 30°,and usually less than about 25°.

In a preferred embodiment of the invention, a hydrocarbon oil issuccessively passed through at least two reaction zones, each containinga different hydroprocessing catalyst, at a temperature of about 500° F.to about 900° F. and at a LHSV of about 0.05 to about 3.0 and in thepresence of hydrogen at a partial pressure about 500 to about 3,000p.s.i.g., employed at a recycle rate of about 1,000 to about 15,000scf/bbl. Although the catalyst of the invention may be employed ineither the first or second reaction zone, preferably it is utilized inthe first reaction zone. The catalyst of the invention is usuallyemployed to promote a high degree at demetallization of the hydrocarbonoil while also maintaining a suitable degree of desulfurization.Conversely, the second hydroprocessing catalyst, while maintaining asuitable degree of demetallization, is primarily employed to promote ahigh degree of desulfurization so that the effluent hydrocarbon oil fromthe second reaction zone has a substantially reduced sulfur andcontaminant metals content. Usually the second catalyst contains one ormore hydrogenation metal components on a porous refractory oxide supportmaterial, and as compared to the catalyst of the invention, has both (1)a lower percentage of the total pore volume in pores of diameter fromabout 180 to about 220 angstroms and (2) a lower average pore diameter(i.e., below about 180 angstroms).

In another preferred embodiment of the invention, a hydrocarbon oilcontaining at least about 50 ppmw of total contaminant metals is firstcontacted at a temperature about 600° F. to about 850° F. and at a LHSVabout 0.1 to about 1.5 with a catalyst of the invention having asubstantial capacity for accumulating contaminant metals. The resultantproduct is subsequently contacted with a second catalyst capable ofremoving both sulfur and contaminant metals. The second catalyst has atleast about 80 percent of the total pore volume in pores of diameterfrom about 100 angstroms to about 200 angstroms and a surface area fromabout 100 m² /gram to about 200 m² /gram. The hydrocarbon oil iscontacted with both catalysts, in two stage operation, in the presenceof hydrogen at a partial pressure about 1,000 to about 2,500 p.s.i.g.and employed at a recycle rate of about 2,000 to about 10,000 scf/bbl.The other catalyst has an average pore diameter at least about 15angstroms smaller than the demetallization catalyst of the invention andalso has a lower percentage of the total pore volume in pores ofdiameter from about 180 to about 220 angstroms. Both catalysts containone or more Group VIII metal components and/or one or more Group VIBmetal components on an alumina-containing porous refractory oxidematerial so that essentially all pores are of diameter greater than 100angstroms, with less than 10 percent of the total pore volume being inpores of diameter greater than 300 angstroms, and with at least about 35percent of the total pore volume being in pores of diameter from about150 angstroms to about 200 angstroms. The product hydrocarbon obtainedfrom this two-stage process typically contains at least about 60percent, and often contains at least 85 percent less contaminant metalsand sulfur than the hydrocarbon oil feedstock.

The catalyst of the invention has a capacity for accumulating asubstantial amount of contaminant metals from a metals-containinghydrocarbon oil during hydroprocessing. Although contaminant metals arecontinuously deposited on the surface and in the pores of the catalystduring the course of hydroprocessing, the useful life of the catalystmay be maintained until the catalyst has gained weight due toaccumulated contaminant metals, calculated as the free metals, to theextent of at least about 25 weight percent, usually at least about 50weight percent, and often times at least about 100 weight percent of theweight of the original catalyst in the oxide form. (I.e., calculated asthe free metals, the contaminant metals deposited in the catalystincrease the catalyst weight in the oxide form to a factor of at leastabout 1.25, usually at least about 1.50 and often times at least about2.00.)

The invention is further illustrated by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limiting the scope of the invention defined by the appendedclaims.

EXAMPLE I

Catalyst A, prepared in accordance with the invention, is tested todetermine its demetallization activity against a reference catalystconsisting of particles of a commercially available demetallizationcatalyst.

Catalyst A is prepared as follows: 96 grams of alumina support particleshaving the physical characteristics summarized in TABLE III areimpregnated with 85 ml of an aqueous solution containing 17 grams ofammonium heptamolybdate [(NH₄)₆ Mo₇ O₂₄.4H₂ O] and 17.5 grams of cobaltnitrate [Co(NO₃)₂.6H₂ O]. After aging for 2 hours, the catalyst is driedat 110° C. and calcined at 1,200° F. in flowing air. A final catalyst isproduced having a nominal composition as follows: 12.0 weight percent ofmolybdenum components, calculated as MoO₃, 4.0 weight percent of cobaltcomponents, calculated as CoO, with the balance comprising gammaalumina.

The reference catalyst is a commercially available demetallizationcatalyst and is produced having a nominal composition as follows: 12.0weight percent of molybdenum components, calculated as MoO₃, 4.0 weightpercent of cobalt components, calculated as CoO, with the balanceconsisting essentially of silica-containing gamma alumina, the SiO₂content being about 1.0 weight percent of the entire catalyst and about1.2 weight percent of the support.

The final catalysts, A and the reference catalyst, and the aluminasupport from which Catalyst A is prepared, have the physicalcharacteristics summarized in Table III.

                  TABLE III                                                       ______________________________________                                        PHYSICAL CHARACTERISTICS                                                      Reference                   Alumina                                           Catalyst        Catalyst A  Support                                                   Pore            Pore        Pore                                              Vol-            Vol-        Vol-                                      Pore    ume     % of    ume   % of  ume   % of                                Diameter,                                                                             cc/     Total   cc/   Total cc/   Total                               Angstroms                                                                             gram    p.v.    gram  p.v.  gram  p.v.                                ______________________________________                                        <40     0       0       0     0     0     0                                   40-60   .19     37      0     0     0     0                                   60-80   .12     23      0     0     0     0                                    80-100 .03     5       0     0     0     0                                   100-120 .005    1       0     0     .03   4                                   120-140 .005    1       .02   3     .06   7                                   140-160 .005    1       .04   5     .27   32                                  160-180 .002    1       .07   10    .18   21                                  180-200 .002    0       .13   18    .12   15                                  200-220 .002    0       .25   35    .06   7                                   220-240 .002    0       .10   14    .04   4                                   240-260 .002    1       .03   4     .01   2                                   260-280 .002    0       .01   1     .015  1                                   280-300 .003    1       .015  2     .005  1                                   300-400 .007    1       .02   2     .01   1                                   400-500 .005    1       0     0     .01   1                                   <500    .14     27      .04   6     .03   4                                   TOTAL   0.52            0.725       .84                                       PORE                                                                          VOLUME                                                                        SURFACE 300             140         153                                       AREA                                                                          m.sup.2 /gram                                                                 ______________________________________                                    

Catalyst A and the reference catalyst are each presulfided for about 16to about 20 hours by contact with a gas consisting of 90 volume percentH₂ and 10 volume percent H₂ S flowing at 4.4 SCFH at one atmospherepressure. The temperature during the presulfiding is initially at roomtemperature, is increased gradually until 700° F. is reached, and thenlowered to 550° F., at which time the catalyst is contacted with thefeedstock.

Catalyst A and the reference catalyst are then tested to determine theirhydrodemetallization and hydrodesulfurization activities and temperatureincrease requirements (TIR), i.e., stability (or resistance todeactivation). The presulfided catalysts, A and the reference, are eachcharged in separate runs to a reactor and utilized at 740° F. tohydrodesulfurize an Iranian atmospheric residua feedstock having thecharacteristics shown in Table IV below under the following conditions:2,000 p.s.i.g. total pressure, 1.0 LHSV, a mass velocity of 220 lbs/hrft² and a hydrogen rate of 6,000 SCF/B.

                  TABLE IV                                                        ______________________________________                                        FEEDSTOCK PROPERTIES                                                          Feed Description Iranian Atmospheric Residua                                  ______________________________________                                        Gravity, °API                                                                           16.6                                                         Sulfur, wt. %    2.61                                                         Nitrogen, wt. %  0.347                                                        Vanadium, ppm    113                                                          Nickel, ppm      37                                                           Ash, ppm         230                                                          Carbon Residue, D-189, wt. %                                                                   6.9                                                          Asphaltenes, (UTM-86), wt. %                                                                   6.1                                                          Pour Point, °F.                                                                         +65                                                          ASTM D-1160 Distillation, °F.                                          IBP              505                                                          5                627                                                          10               682                                                          20               753                                                          30               820                                                          40               872                                                          50               942                                                          60               1,033                                                        Max              1,035                                                        Rec              61.0                                                         ______________________________________                                    

A portion of the feedstock is passed downwardly through each reactor andcontacted with the described catalysts in a single-stage, single-passsystem with once-through hydrogen such that the effluent metalsconcentrations is maintained at about 15 ppm, equivalent to about 90percent demetallization. The calculated temperatures required for thisconversion, as adjusted from actual operating reactor temperatures, issummarized in Table V.

                  TABLE V                                                         ______________________________________                                        DEMETALLIZATION TEMPERATURES REQUIRED, °F.                                      5      10       15   20     25   30                                  Catalysts                                                                              Days   Days     Days Days   Days Days                                ______________________________________                                        A        746    757      764  769    773  775                                 Ref      760    776      785  793    797  805                                 ______________________________________                                    

In view of the data in Table V relative to demetallization of thefeedstock, catalyst A is noticeably more active than the referencecatalyst during the entire run. After 30 days, catalyst A is about 30°F. more active than the reference catalyst.

EXAMPLE II

Catalyst B, prepared in accordance with the invention, is tested todetermine its demetallization activity against the reference catalyst ofExample I. Catalyst B is prepared in the same manner as Catalyst A ofExample I except 12.5 grams of citric acid are also contained in theaqueous impregnation solution. A final catalyst is produced having thesame nominal composition of molybdenum, cobalt and alumina as Catalyst Aof Example I and having the physical characteristics summarized in TABLEVI.

                  TABLE VI                                                        ______________________________________                                        PHYSICAL CHARACTERISTICS                                                                     Catalyst B                                                     Pore             Pore     % of                                                Diameter,        Volume   Total                                               Angstroms        cc/gram  p.v.                                                ______________________________________                                        <100             0        0                                                   100-200          .005     1                                                   120-140          .01      1                                                   140-160          .03      5                                                   160-180          .04      6                                                   180-200          .11      16                                                  200-220          .17      25                                                  220-240          .15      22                                                  240-260          .07      11                                                  260-280          .02      3                                                   280-300          .02      3                                                   300-400          .025     3                                                   400-500          .01      2                                                   >500             .01      2                                                   TOTAL PORE       0.67                                                         VOLUME                                                                        SURFACE          136                                                          AREA                                                                          m.sup.2 /gram                                                                 ______________________________________                                    

The reference catalyst and catalyst B are tested with the same feedstockin the same manner as Example I, except the condition of mass velocityis 400 lbs/hr ft². The calculated temperatures required for about 90percent demetallization, as adjusted from actual operating temperatures,is summarized in Table VII.

                  TABLE VII                                                       ______________________________________                                        DEMETALLIZATION TEMPERATURES REQUIRED, °F.                                      5         10     20      30   40                                     Catalysts                                                                              Days      Days   Days    Days Days                                   ______________________________________                                        B        735       752    770     777  785                                    Ref      751       766    782     790  798                                    ______________________________________                                    

In view of the data in Table VII relative to demetallization of thefeedstock, catalyst B is noticeably more active than the referencecatalyst during the entire run. During essentially the entire run of 40days, catalyst B is between about 12° F. and 16° F. more active than thereference catalyst.

EXAMPLE III

Catalyst A of Example I is tested for 227.5 consecutive days at variousconditions to determine its capacity for accumulating contaminant metalsfrom metals containing hydrocarbon oils.

The catalyst is presulfided in the same manner as described in ExampleI, then contacted for the first 125.1 days with the Iranian feedstockhaving the same characteristics as in Example I and subsequentlycontacted for another 102.4 days with a Kuwait feedstock having thecharacteristics shown in Table VIII below.

                  TABLE VIII                                                      ______________________________________                                        FEEDSTOCK PROPERTIES                                                          Feed Description Kuwait Atmospheric Residua                                   ______________________________________                                        Gravity, °API                                                                           16.8                                                         Sulfur, wt. %    3.70                                                         Nitrogen, wt. %  0.207                                                        Vanadium, ppm    49                                                           Nickel, ppm      14                                                           Ash, ppm         --                                                           Carbon Residue, D-189, wt. %                                                                   8.7                                                          Asphaltenes, (UTM-86), wt. %                                                                   6.9                                                          Pour Point, ° F.                                                                        +30                                                          ASTM D-1160 Distillation, °F.                                          IBP              487                                                          5                610                                                          10               664                                                          20               739                                                          30               805                                                          40               863                                                          50               937                                                          60               1,028                                                        Max              1,108                                                        Rec              73.0                                                         ______________________________________                                    

The presulfided catalyst is charged to a reactor and utilized at 740° F.to demetallize the feedstocks under the conditions of 2,250 p.s.i.g.total pressure and a hydrogen rate of 10,000 SCF/B. A portion of thefeedstock is passed downwardly through the reactor and contacted withthe catalyst in a single-stage, single-pass system with once-throughhydrogen such that effluent metals concentrations are maintained atabout 15 ppm over the first 125.1 days of the run with the Iranianfeedstock and at about 6 ppm over the remainder of the run (102.4 days)with the Kuwait feedstock, i.e., equivalent to about 90 percentdemetallization.

The calculated temperatures for about 90 percent demetallization, asadjusted for actual operating reactor temperature, at different spacevelocities (LHSV) for indicated time intervals during the 227.5 day runare summarized below in Table VIII. The original catalyst, in themonoxide and trioxide form of the cobalt and molybdenum metals,respectively, exhibits an increase in weight during the 227.5 days ofthe run, due to the additional weight of the deposited contaminantmetals, calculated as the free metals. The average percentage of weightincrease of the catalyst, due to contaminant metals deposition, for theindicated time intervals, as compared to the original catalyst weight,is also summarized in TABLE IX.

                  TABLE IX                                                        ______________________________________                                                                          Average Weight                                                                Percent Increase                            Days                              of Catalyst                                 of                      Temp. for 90%                                                                           Due to Metals                               Run   Feedstock LHSV    Demetallization                                                                         Deposition                                  ______________________________________                                        1     Iranian   1.0     746                                                   30    (Table    1.0     780       18.0                                              VII)                                                                    31              0.5     744                                                   40              0.5     745       21.0                                        41              1.0     782                                                   50              1.0     783       24.5                                        51              0.5     746                                                   125.1           0.5     778       45.5                                        125.1 Kuwait    0.5     768                                                   140   (Table    0.5     769       47.0                                              VIII)                                                                   141             0.6     781                                                   179             0.6     775       50.5                                        180             1.2     824                                                   227.5           1.2     830       65.5                                        ______________________________________                                    

In view of the data in TABLE IX catalyst A exhibits a capacity foraccumulating a substantial amount of contaminant metals frommetals-containing hydrocarbon feedstocks. After 227.5 days, during whichcatalyst A is utilized for hydroprocessing the metals-containingfeedstocks, approximately a 65.5 average weight percent increase incatalyst A is observed, due to the accumulation of contaminant metals onthe catalyst. Furthermore, even after 227.5 days there is no sign ofmuch change in the effluent metals concentrations as indicated by only a6° F. increase over the last 47.5 days of the run.

The final average percentage of deposited metals may be determined fromanalysis of samples of catalyst removed from the top, middle and bottomportions of the reactor after 227.5 days. Analysis of samples ofcatalyst A removed from the top of the catalyst bed reveal a contaminantmetals deposition that is about 101 weight percent of original catalystA, i.e., the metals deposition has increased the catalyst weight by morethan a factor of 2, and specifically by about 2.01.

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many obvious modifications can be made, and it is intended toinclude within this invention any such modifications as will fall withinthe scope of the invention as defined by the appended claims.

I claim:
 1. A catalyst comprising one or more active metal components ona porous refractory oxide, said catalyst having at least about 60percent of the total pore volume distributed in pores of diameter fromabout 180 angstroms to about 240 angstroms, with essentially all poresbeing of diameter greater than about 100 angstroms, and with less thanabout 10 percent of the total pore volume being in pores of diametergreater than 300 angstroms.
 2. The catalyst defined in claim 1 whereinsaid active metal components comprise Group VIB and Group VIII metals.3. The catalyst defined in claim 2 wherein said Group VIB metal isselected from the group consisting of molybdenum and tungsten.
 4. Thecatalyst defined in claim 2 wherein said Group VIII metal is selectedfrom the group consisting of cobalt and nickel.
 5. The catalyst definedin claim 1 having a surface area greater than about 100 m² /gram.
 6. Thecatalyst defined in claim 1 with an average pore diameter greater thanabout 180 angstroms.
 7. The catalyst defined in claim 2 furthercomprising up to about 10 weight percent of Group VIII metal components,calculated as the monoxides, and up to about 30 weight percent of GroupVIB metal components, calculated as the trioxides.
 8. The catalystdefined in claim 1 having an average pore diameter from about 180angstroms to about 220 angstroms.
 9. The catalyst defined in claim 1having a surface area from about 100 m² /gram to about 200 m² /gram. 10.The catalyst defined in claim 1 having a total pore volume from about0.25 cc/gram to about 1.2 cc/gram.
 11. The catalyst defined in claim 1with at least about 65 percent of the total pore volume being in poresof diameter from about 180 angstroms to about 240 angstroms.
 12. Thecatalyst defined in claim 1 with greater than about 90 percent of thetotal pore volume being in pores of diameter greater than about 150angstroms.
 13. The catalyst defined in claim 1 wherein said porousrefractory oxide comprises alumina.
 14. The catalyst defined in claim 13wherein said alumina consists essentially of gamma alumina.
 15. Thecatalyst defined in claim 1 having a capacity for accumulatingcontaminant metals from a metals-containing hydrocarbon oil such thatthe weight of said catalyst is increased by at least about 25 percentdue to accumulated contaminant metals, calculated as the free metals.16. The catalyst defined in claim 1 with less than about 25 percent ofthe total pore volume being in pores greater than about 240 angstroms.17. A catalyst comprising at least one active Group VIB metal componenton a porous refractory oxide comprising alumina, said catalyst with anaverage pore diameter greater than about 180 angstroms, with at leastabout 60 percent of the total pore volume distributed in pores ofdiameter from about 180 angstroms to about 240 angstroms, withessentially all the pores being of diameter greater than about 100angstroms, and with less than about 10 percent of the total pore volumebeing in pores of diameter greater than about 300 angstroms.
 18. Thecatalyst defined in claim 17 wherein said alumina consists essentiallyof gamma alumina.
 19. The catalyst defined in claim 17 wherein saidporous refractory oxide contains at least about 90 weight percent ofalumina.
 20. The catalyst defined in claim 17 wherein less than about 25percent of the total pore volume being in pores of diameter greater thanabout 240 angstroms.
 21. The catalyst defined in claim 17 wherein saidGroup VIB metal is selected from the group consisting of molybdenum andtungsten.
 22. The catalyst defined in claim 17 further comprising atleast one Group VIII metal component.
 23. The catalyst defined in claim22 wherein said Group VIII metal is selected from the group consistingof cobalt and nickel.
 24. The catalyst defined in claim 22 wherein saidGroup VIB metal comprises molybdenum and said Group VIII metal componentcomprises cobalt.
 25. The catalyst defined in claim 22 wherein saidGroup VIB metal comprises tungsten and said Group VIII metal componentcomprises nickel.
 26. The catalyst defined in claim 22 furthercomprising up to about 10 weight percent of Group VIII metal components,calculated as the monoxides, and up to about 30 weight percent of GroupVIB metal components, calculated as the trioxides.
 27. The catalystdefined in claim 17 having an average pore diameter from about 180angstroms to about 220 angstroms.
 28. The catalyst defined in claim 17having a capacity for accumulating contaminant metals from ametals-containing hydrocarbon oil such that the weight of said catalystis increased by at least about 50 percent due to accumulated contaminantmetals, calculated as the free metals.
 29. The catalyst defined in claim17 having a surface area from about 100 m² /gram to about 200 m² /gram.30. The catalyst defined in claim 17 having a total pore volume fromabout 0.4 cc/gram to about 0.9 cc/gram.
 31. The catalyst defined inclaim 17 with greater than about 95 of the total pore volume being inpores of diameter greater than about 140 angstroms.
 32. A catalystuseful for removing contaminant metals from a hydrocarbon oil comprisinga Group VIB and a Group VIII metal component on a porous refractoryoxide consisting essentially of gamma alumina, said catalyst with anaverage pore diameter from about 180 to about 220 angstroms, with atleast about 65 percent of the total pore volume distributed in pores ofdiameter from about 180 angstroms to about 240 angstroms, withessentially all the pores being of diameter greater than 100 angstroms,with greater than about 95 percent of the total pore volume being inpores of diameter greater than about 140 angstroms, with less than about10 percent of the total pore volume being in pores of diameter greaterthan about 300 angstroms, with less than about 25 percent of the totalpore volume being in pores of diameter greater than about 240 angstroms,with a surface area from about 100 m² /gram to about 200 m² /gram, andwith a total pore volume between about 0.45 cc/gram and about 0.8cc/gram.
 33. The catalyst defined in claim 32 wherein said Group VIBmetal is selected from the group consisting of molybdenum and tungsten.34. The catalyst defined in claim 32 wherein said Group VIII metal isselected from the group consisting of cobalt and nickel.
 35. Thecatalyst defined in claim 32 wherein said Group VIB metal comprisesmolybdenum and said Group VIII metal component comprises cobalt.
 36. Thecatalyst defined in claim 32 wherein said Group VIB metal comprisestungsten and said Group VIII metal component comprises nickel.
 37. Thecatalyst defined in claim 32 further comprising about 2 to about 6weight percent of Group VIII metal components, calculated as themonoxides, and about 8 to about 26 weight percent of Group VIB metalcomponents, calculated as the trioxides.
 38. The catalyst defined inclaim 32 having an average pore diameter from about 190 angstroms toabout 210 angstroms.
 39. The catalyst defined in claim 32 having acapacity for accumulating contaminant metals from said hydrocarbon oilsuch that the weight of said catalyst is increased by at least about 100percent due to accumulated contaminant metals, calculated as the freemetals.
 40. A catalyst prepared with a porous refractory oxide support,said support comprising a narrow pore size distribution with essentiallyall pores being of diameter greater than about 100 angstroms, with lessthan about 10 percent of the total pore volume being in pores ofdiameter greater than 300 angstroms, and with at least about 60 percentof the total pore volume being in pores of diameter distributed over anarrow range of about 60 angstroms within the 100 angstrom range ofabout 140 to about 240 angstroms.
 41. The catalyst defined in claim 40wherein said support has a total pore volume from about 0.5 to about 2.0cc/gram.
 42. The catalyst defined in claim 40 wherein said support has asurface area greater than about 100 m² /gram.
 43. The catalyst definedin claim 40 wherein said support has an average pore diameter greaterthan about 160 angstroms.
 44. The catalyst defined in claim 40 furthercomprising up to 30 weight percent of a Group VIB metal component,calculated as the trioxide.
 45. The catalyst defined in claim 40 furthercomprising up to 10 weight percent of a Group VIII metal component,calculated as the monoxide.
 46. The catalyst defined in claim 40 whereinsaid support consists essentially of gamma alumina.
 47. A method forpreparing a catalyst comprising a porous refractory oxide support, saidmethod comprises compounding one or more active metals with saidsupport, said support comprising a narrow pore size distribution withessentially all pores being of diameter greater than about 100angstroms, with less than about 10 percent of the total pore volumebeing in pores of diameter greater than 300 angstroms, and with at leastabout 60 percent of the total pore volume being in pores of diameterdistributed over a narrow range of about 60 angstroms within the 100angstrom range of about 140 to about 240 angstroms.